1. Field of the Invention
The present invention relates generally to an electronically controlled automatic transmission capable of independently learning the fluid fill volumes of its friction elements and, more particularly, to a volume learn sequence which enables the transmission to learn these volumes before the vehicle has been driven.
2. Discussion
Land vehicles generally require three basic components: an engine, a power train and wheels. The engine produces force by converting chemical energy contained in a liquid fuel into the mechanical energy of motion. The power train transmits this resultant force to the wheels to provide movement of the vehicle. The main component of the power train is the transmission which converts engine torque and speed in accordance with the tractive-power demand of the vehicle. The transmission also controls the direction of rotation applied to the wheels so that the vehicle may be driven both forward and backward. A torque converter transmits power from the rotating engine crankshaft to the input member of the transmission.
One advanced type of transmission is a four speed electronically controlled automatic transmission with overdrive. One example of an electronic automatic transmission of this type is described in U.S. Pat. No. 4,875,391, entitled "An Electronically-Controlled, Adaptive Automatic Transmission System", issued on Oct. 24, 1989 to Leising et al. This patent is owned by the Assignee of the present application and is incorporated herein by reference. However, it should be appreciated that the principles of the present invention are not limited to any particular electronically controlled automatic transmission, and that the present invention may be applicable to a wide variety of other similar powertrain configurations.
In this type of electronic automatic transmission, a series of clutches or friction elements provide a means for application and release of separate members to and from each other during the flow of power through the transmission. These clutches thereby constitute the means by which gears within the transmission are selectively engaged or disengaged from either the engine crankshaft or the transmission case. Four speed transmissions of this type generally include four elements or clutches which are applied or engaged in various combinations in relation to each of the vehicle's gears. Those in the present transmission include an underdrive clutch (applied in first, second and third gears), an overdrive clutch (applied in third and fourth gears), a two/four shift clutch (applied in second and fourth gears) and a low/reverse clutch (applied in first and reverse gears). Each of these clutches generally includes a plurality of alternating clutch plates and clutch disks which, when applied, engage one another and which, when the clutch is not applied, are free to move or rotate relative to each other.
To apply each of these clutches, an electronically controlled hydraulic fluid actuating device such as a solenoid-actuated valve is used. There is typically one valve for each clutch, an underdrive clutch solenoid-actuated valve, an overdrive clutch solenoid-actuated valve, a two/four shift solenoid-actuated valve and a low/reverse solenoid-actuated valve. These valves each control fluid flow to a respective clutch apply cavity. The flow of fluid into a clutch apply cavity results in the application or engagement of that clutch. Fluid flow is enabled by the opening of the solenoid-actuated valve in response to command or control signals received by the solenoid from an electronic control system.
The electronic control system typically includes a microcomputer-based transmission control module capable of receiving input signals indicative of various vehicle operating conditions such as engine speed, torque converter turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressures, a driver selected gear or operating condition (PRNODDL), engine coolant temperature and/or the ambient air temperature. Based on the information contained in these signals, the controller generates command or control signals for causing the actuation of each of the solenoid-actuated valves which regulate the application and release of fluid pressure to and from the apply cavities of the clutches or frictional units of the transmission. Accordingly, the controller is programmed to execute predetermined shift schedules stored in a memory of the controller through appropriate command signals to the solenoid-actuated valves.
Although in the manufacture of such transmissions each of the transmission components is machined to precise predefined dimensions, manufacturing tolerances or build variations often result in components having slightly larger or smaller dimensions. This may ultimately affect the hydraulic fluid fill volumes of each of the various clutches, or in other words, the volume of fluid which must be displaced to effectively apply or engage that clutch. These fluid fill volumes are used by the electronic transmission controller to effectively control fluid application to each element in order to provide an optimum shift quality or feel.
After a transmission is manufactured, a nominal fill volume for each element may be stored in a permanent non-volatile memory location within the transmission controller for use in effectively controlling this fluid flow. The transmission controller uses this stored value in controlling fluid application to each of the clutches. However, as discussed above, this stored nominal valve may deviate from the actual fill volume due to build variations or component wear. This information is used by the transmission controller in carrying out its shifts and therefore may result in a less than optimum shift quality.
The controller of a transmission of the type to which the present invention is directed, therefore, is programmed to update this originally stored value or "learn" from the results of its operation. The nominal volume value is stored in a non-volatile memory location but a learned volume value is stored for use by the transmission control logic in a battery backed RAM. This learned value is continuously updated as the vehicle is driven and is thereafter used by the transmission controller to precisely control fluid flow and fully optimize shift quality. A transmission having this capability is described in detail in U.S. Pat. No. 4,982,620 to Holbrook, et al. This patent is also assigned to the Assignee of the present application and is also incorporated herein by reference.
However, this "learning" currently only takes place when the vehicle is driven, and therefore does not impact initial shift quality, or the shift quality the first time the vehicle is actually driven. There is therefore a need for a means by which these hydraulic fluid fill volumes can be learned prior to the vehicle being driven.